> > Largish stepper motors can be had fairly cheaply. At the > RPM you're > > after they'd work nicely. Downside is you need to make drivers for > > them. Not hard, but a bit of a nuisance and pushes the cost up > > somewhat. The simplest driver is for unipolar motor (6 > wire) and is 4 > > fets and a bit of logic. > > I've trouble finding a stepper motor that can produce 50 Nm > (7000+ ozf.in). > The biggest I found have a holding torque of 40 Nm (5700 > ozf.in), which is a bit more than what we have now (as stall torque). > http://www.anaheimautomation.com/hightorque.htm > > Are there stronger stepper motors? > > How does the holding torque of a stepper motor relate to the > stall torque of a DC motor? One site says that "dynamic > torque" is about 70% of holding torque. Is "dynamic torque" > what I have available to move something? (I know that the > available torque goes down with speed, but since I'm working > at around 1 rot/s, it seems that is very slow for a typical > stepper motor and it develops its maximum torque.) Ok, your definition of 'largish' is different to mine :) There are bigger steppers, the next size up from a NEMA42 is a NEMA66, but it starts getting a bit silly. The body of that is bigger than a CD-ROM! You could bolt a gearhead to the stepper, at low RPM you tend not to loose too much torque. Given the prices on this page , that's probably not an option. Not sure what they mean by dynamic torque, as you say torque varies with speed. Most steppers have a torque curve that remains fairly flat up to a certain speed, and then falls off rapidly, a bit like a knee. Maybe the 70% refers to that point. Looks like your stuck with trading speed for torque, get a motor and gear it down. Servos on CNC machines are usually geared down (say 1:5), so pulleys & belts are common. 50Nm is a lot of torque, what are you making? Tony -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist